If you move an NPC into your household they are no longer employed, but I had one Sim that married a male maid and none of their children made messes even when they were not given the
neat trait.
With the introduction of Ambitions, it is now possible to play your own fireman and the children do sometimes inherit that hidden trait. It may even skip a generation as my fireman's three sons didn't inherit the
pyromaniac trait but one of his grandsons did.
Since these are hidden traits, it may be random whether the trait is inherited or not. Hope this helps.